Swampfire is the Omnitrix's DNA sample of a Methanosian[2][1] from the planet Methanos.[Bandai 1]

Swampfire is a humanoid, plant-like alien that has an overall green and black colored body encrusted with muck, mostly with a red flame-patterned head and root-like feet, seemingly holding black rocks. His eyes are oval-shaped with points at each end with pupils copying the shape but are smaller. Also, his shoulders and head have red petals and his elbows and legs have green frills sticking out. Swampfire is taller than an average human and has a distinct rotten stench that worsens with heat.

In Alien Force and Ultimate Alien, Swampfire wore the original Omnitrix/Ultimatrix symbol on his chest.

In Omniverse, Swampfire's first design was similar to his previous appearance, except for having five fingers on his hands. Swampfire's skin was olive green, and his arms were larger. The red petals on his shoulders, along with the green thorns on his body, were thinner and longer. His torso design changed, splitting the black parts on his waist into two. The Omnitrix symbol also moved from his chest to his stomach.

Swampfire's first stage of blossoming was more muscular than his earlier design. He also lost his pupils, one of his red petals on each shoulder, and a green frill from each leg. The lines on his neck thinned and the lines on his chest moved upward and into a pointed down angle. His green color was also a shade lighter than his olive green.

Swampfire's second stage of blossoming had more muscle with the black lines being removed from his chest entirely. His red petals formed into a red thorn shape, with two being on each arm. The necklines were triangular and his shade of green was lime green. His face resembled his fully matured form except that instead of orange surrounding the eyes, there was black surrounding them.

As of Charmed, I'm Sure, Swampfire's second appearance, or his blossomed/matured form, is plant-like, but with major changes. He looks more muscular and taller, his skin color is now light green, his face is now colored yellow, red, and orange, his pupils are gone and his chin is more visible. His hands are now colored black, with four yellow claws (with spikes on the knuckles), and yellow holes in the palms, used to unleash his fire powers. He has six red horns with yellow spots (aesthetically resembling flames); two on each forearm, and one on each shoulder, as well as a green horn on each foot, knee, and elbow. He now has a large collar raised up around his neck, which is yellow on the inside. The Omnitrix symbol is still on his stomach.